1. Field of the Invention
The present invention relates to a tunnel magnetoresistive effect (TMR) element for reading a signal representing a magnetic field intensity in a magnetic recording medium, to a thin-film magnetic head with the TMR read head element, and to a magnetic disk drive apparatus with the thin-film magnetic head.
2. Description of the Related Art
In order to satisfy the demand for higher recording density and downsizing in a hard disk drive (HDD) apparatus, higher sensitivity and larger output of a thin-film magnetic head are required. In order to meet this requirement, a thin-film magnetic head with a TMR read head element has been put to practical use.
In the thin-film magnetic head with such TMR read head element, it is necessary to decrease both resistance and capacitance of a read head circuit in order to be adaptive at high frequencies. Decreasing the resistance of the TMR read head element itself is effective to do this. This can easily be accomplished by reducing a thickness of a tunnel barrier layer.
However, the thin tunnel barrier layer causes problems as follows:
(1) the life of an element is reduced due to an increase in pin-holes in the tunnel barrier layer;
(2) a magnetic coupling between a magnetization fixed layer and a magnetization free layer in a TMR multiplayer increases causing an increase in noise at read output;
(3) it is difficult to control a process of fabricating a uniformly thin tunnel barrier layer; and
(4) a magnetoresistive effect (MR) ratio decreases.
Therefore, it is necessary to reduce a sheet resistivity of the tunnel barrier layer without making it thin. In addition, it is required to maintain a high MR ratio.
U.S. Pat. Nos. 6,771,473 and 7,042,686 disclose a technique for realizing a low junction resistance and a high MR ratio. According to this technique, an intermediate layer containing at least three elements selected from Groups 2 to 17, which elements include at least one of F, O, N, C and B is used as a tunnel barrier layer.